Bump actions/checkout from 5 to 6 in /.github/workflows (#29)

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
     name: Lint Rust code
     runs-on: windows-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Cargo fmt
         run: cargo fmt --all -- --check
       - name: Cargo clippy
@@ -23,7 +23,7 @@ jobs:
     name: Build-test MSRV (1.74) with minimal crate dependencies
     runs-on: windows-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@nightly
       - name: Generate minimal-version dependencies
         run: cargo -Zminimal-versions generate-lockfile
@@ -34,7 +34,7 @@ jobs:
   generate:
     runs-on: windows-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Checkout submodule
         # Manually update submodules with --checkout because they are configured with update=none and will be skipped otherwise
         run: git submodule update --recursive --init --force --checkout

.github/workflows/publish.yaml

@@ -10,6 +10,6 @@ jobs:
     if: github.repository_owner == 'Traverse-Research'
     runs-on: windows-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Publish
         run: cargo publish --token ${{ secrets.cratesio_token }}